1. 根据句意及汉语提示完成句中所缺单词。

1. （1） The boy collected  (瓶子) for money to buy some books.

3. （2） Obama is the  (总统) of the USA

5. （3） At the school  (大门) Jim met his old friend Sam.

7. （4） The knife is made of  (金属). It feels smooth and cold.

9. （5） In order to protect the environment, it's important for us to  (回收) used books and paper.